The present invention relates generally to diode pumped laser systems, and more particularly, to an active energy control circuit and method employing pulsewidth modulation for use with such diode pumped laser systems.
Prior laser systems use flashlamp pumping and an associated active control of the laser output energy by increasing or decreasing the voltage and current to the flashlamp without changing the pulsewidth. Flashlamp pumped laser systems are less efficient than diode pumped lasers, requiring a larger power supply, and more thermal management in addition to requiring more input power to generate a similar laser output. The technique used in the flashlamp systems for active laser output energy control is inappropriate for a diode pumped system.
Diode pumped laser systems require keeping the current to the pump diodes below a maximum current damage level. The most efficient operating point however is near that maximum current level. In one laser development program of the assignee of the present invention, the actual setting for efficient laser operation is approximately 80 Amps, when the maximum current level is approximately 90 Amps. The approach previously used on this program was to use a current regulator (Buck converter) to keep the current regulated at an efficient set point below the damage level. The typical pump pulse to the laser diodes for a NdYag laser is on the order of 80 Amps for 200 microseconds. The active feedback for flashlamp pumping described above is not appropriate since increasing and decreasing the current to the pump diodes could result in damage to the pump diodes or loss in efficiency.
Accordingly, it is an objective of the present invention to provide for an active laser control system and method that employs feedback sensing of the optical output energy and output control of the electrical pulsewidth to pump diodes of the laser system to create an active energy control loop for maintaining diode pumped laser output energy at a desired level over different pulse repetition frequencies, time, and environmental conditions.